V. Jormalainen et al., Why does herbivore sex matter? Sexual differences in utilization of Fucus vesiculosus by the isopod Idotea baltica, OIKOS, 93(1), 2001, pp. 77-86
Optimal feeding is often constrained by predation avoidance, which may dire
ct feeding to take place on more sheltered, but less profitable, Darts of t
he habitat. Though constrained, feeding preferences and/or digestive capabi
lities should coevolve with the energetic and nutritional needs of the anim
al. These needs, as well as risk taking for these goals, may differ between
the sexes. We studied sexual differences in the utilization of the brown a
lga Fucus vesiculosus by the marine isopod Idotea baltica. In a feeding pre
ference test with small pieces of alga both sexes prefer the apical. newly
grown parts to the basal parts. However, males show stronger preference tha
n females. When isopods are reared on the apical or basal part of the alga
alone, sexes grow differently on these parts. Females gain weight equally w
ell and their intermolt duration is the same on both parts of the alga, whi
le males perform clearly worse on the basal than on the apical part. Despit
e the better quality of the apical parts of the alga, in a grazing experime
nt in a "semi-natural" environment with whole bushes of F. vesiculosus also
the basal parts are consumed, and even preferred over apical parts by fema
les. We suggest that feeding preferences are subordinate to microhabitat ch
oice, and therefore predation avoidance constrains optimal feeding. We hypo
thesize that the better ability of females than that of males to utilize th
e basal parts of the alga for growth is a co-adaptation to their risk-avers
e general reproductive strategy. We discuss the sexual differences in host
plant utilization in the context of reproductive strategies of the sexes, e
specially different risk sensitivity of foraging, and its potential consequ
ences on plant-herbivore interaction.